Heh. Of course for AS's lacking usptreams, a more sensible sort of Local Preference hierarchy might be... Customer Prefered Customer Customer Backup Private Peers Congested Private Peers (perish the thought!) Good Public Peers (usually gigE exchange points) Bad Public Peers (Used to be FDDI, now ATM, i guess :) This is the usual ranking system used, with each category having both a local pref (and occasionally a range of LPs), and a destinctive community value. Although 701 has mechanisms for handling this (which work), the best approach for most folks who have both peers and customers, is to pref your customers, to ensure that their routes are always chosen in case of prepending. There are several reasons for this... 1 - Customers generally WANT traffic from directly connected networks. They also want to be able to prepend in order to balance traffic. 2 - Selecting a route through a peer, instead of a customer could adversely effect both your peering traffic balance, and your burstable billing model :) One way of accomplishing this sort of thing, if one were completely adverse to Local Preference, would be to use additive MEDs, and adding a large MED cost for peers, and a smaller one for customer routes, at point of ingress. - Daniel Golding
-----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu]On Behalf Of David Barak Sent: Monday, December 17, 2001 10:55 AM To: Mike Leber Cc: nanog@merit.edu; smentzer@mentzer.org; rekoil@semihuman.com; gmartine@nic.gip.net Subject: Re: AS 701 local-pref answer.
Hi,
I don't think AS 701 (or any of its peers) are particularly worried about different best-paths in different regions. This is the old hot-potato/cold-potato discussion, which I don't see a need to re-hash.
Let's pretend that Bob's bait & tackle shop (AS 30,000) is multihomed to AS 701 and AS 1. Bob would probably want AS701 origin traffic to prefer his AS701 link, and his AS1 Origin traffic to prefer his Genuity link. No problem there - they both see a route 1 AS-hop away. The question only comes when Bob wants to have all other traffic prefer one link or the other.
If he chose to prepend his AS to AS701, then he would run the risk of Genuity being the preferred path from AS701, and AS701 would not advertise a path. This would be a useful situation if, for instance, the Genuity link was a DS3, and the 701 link was a T1. If they were equal bandwidth links, and Bob was trying to do traffic-sharing, then that would not be a good solution.
AS 701 does have mechanisa for customers to do this, and their support people are more than happy to assist customers with their routing needs.
By the way, the gentleman who referred to "customers, peers, and upstreams" as useful loc-pref settings should remember that AS701 doesn't have upstreams. :)
David Barak I speak for myself only. "Quis custodes ipsos custodiet?" - Juvenal
--- Mike Leber <mleber@he.net> wrote:
Not to be like Columbo... However, there's just one last question bothering me. Well ok, more than one :)
If it's like mentzer@mentzer.org said and 701 doesn't deterministicly prefer customer routes (customers and peer routes at the same local pref) wouldn't this mean that they wouldn't have consistent route announcments in various parts of their network?
If a customer doesn't set the community to boost the local pref, and 701 truly by default sets customers and peers to 100, then 701 would be announcing varying numbers of routes to the same peer at different locations.
Do they expect consistent route annoucements from their peers?
Many networks out there insist upon this as a requirement when peering.
Mike.
On Sun, 16 Dec 2001, Mike Leber wrote:
Thank you for pointing that out. I was being
much into the statements:
smentzer@mentzer.org wrote:
All the responses I have gotten indicate that UUnet does indeed set local-pref on both customers and peers to 100 (or leave default in this case). Thanks for all the responses...
Especially when the 701 communities were already
Martinez. *DOH*
In other words, 701 transit customers that actually want to ensure their downstream customer routes are announced by 701 had better set the appropriate community so that local pref gets set above 100. By default this is not done.
Pardon me while I get some much needed rest.
Mike.
On Sun, 16 Dec 2001, David Barak wrote:
Mike Leber wrote:
If they set local pref for both peers and customers to 100 how do they ensure that the customer transit routes are announced to peers?
The reason I ask this is because if a customer announces a customer of theirs to you that a peer also has as a customer >you will have equal length routes for the same destination AS. While there are many ways to deterministicly prefer customer routes, local
is the most common.
AS 701 always announces the best route, as their routers know it. Their average AS-path length is under 2, so it doesn't seem to be a problem. If a customer of AS 701 wants to insure that his/her route is advertised in all cases, s/he could send a community which AS701 edge devices could use to manipulate local-preference upward. [this was covered in a previous posting on this topic] I leave it to your imagination whether peers would be
dense and reading way too provided by German pref permitted to
do this.
-David Barak I only speak for myself. "Quis custodes ipsos custodiet?" - Juvenal
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